A magnetic recording read channel converts an analog read channel into an estimate of the user data recorded on a magnetic medium. Read heads and magnetic media introduce noise and other distortions into the read signal that correlate with the written user data. A number of techniques have been proposed or suggested for taking statistical correlations between the written user data and distortions into account in order to improve read channel performance.
Previous techniques that used data dependent statistics to improve detector error rates were unwieldy because they required off-board processing to calculate detector parameters from statistics that were off-loaded from the device. This off-load, calculate, and on-load cycle becomes prohibitively time consuming and complex when the number of distinct data conditions used, and the number of correlation lags used, are large enough to realize significant gains in error rate performance.
A need therefore exists for a method and apparatus for adapting to these data correlations without relying on external calculations or circuits. A further need exists for a method and apparatus that can adapt to these data correlations during normal read operations and provide parameter values to the sequence detector (or to a post-processor acting on AN initial NRZ estimate produced by a sequence detector).